When making castings by pouring moulds with vertical parting surfaces, the moulds will normally be advanced along the pouring track on a precision conveyor, e.g. of the kind described in the DK patent publications Nos. 119,373 and 127,494; in this manner, the moulds or mould parts are placed in mutual abutment in a highly accurate manner, and this accuracy is maintained during the steps of pouring and solidification. After the pouring step, the moulds may be transferred to a conveyor of the kind described in DK-patent publication No. 138,840, making it possible to reduce the total frictional resistance against the movement of the moulds.
For the reasons referred to above, the moulds are frequently transferred at a relatively early stage in the process from the precision conveyor to a second conveyor producing less frictional resistance than the precision conveyor. This second conveyor may possibly be constituted by an endless belt. During the transfer to the second conveyor it must be ensured, either that the casting is sufficiently cooled to avoid the occurrence of cooling defects or deformations, or that the individual moulds are transferred in a manner preventing mutual displacements of the mould parts, possibly being the cause of deformations or cooling defects, respectively. Because of these relationships, the string of moulds will normally be transferred as a solid body through the second conveyor and advanced--still undivided--on the latter, until the castings have been cooled sufficiently, eventually to reach an extraction station.
An alternative to conveying the string of moulds as a continuous string to the extraction station is based on the use of devices to divide or break open the moulds in the mould string, e.g. of the kind shown in DK-B-129,397, in which such a device removes the central part of the moulds together with the castings. This alternative will, however, require the use of complicated equipment, the latter frequently having to be adapted to the particular castings being made and the particular moulds being used at any moment, especially when there is a change in the dimensions. Further, such an intermediate station will produce dust and fragments to be accounted for, as they can constitute a health risk and contribute to increased wear on moving parts.
Normally, however, the string of moulds will be advanced in the form of a continuous string on the second conveyor until the castings are cooled sufficiently for the extraction step. Further, if the second conveyor consists of flexible material incapable of withstanding high temperatures, such as e.g. is the case with endless belts of rubber or plastic material, it must be ensured, either that the castings do not come into contact with the conveyor belt during the extraction, or that the castings are cooled to a temperature not causing damage to the conveyor belt, the latter temperature frequently lying far below the temperature of solidification of the castings, thus requiring a disproportionately long cooling time on the conveyor belt.
A previously known automatic casting machine of the kind referred to above operates in the following manner. The moulds or mould parts are produced in a mould-making station, from which they are conveyed in the form of a closely packed string of moulds by a precision conveyor along a track to a pouring station, in which liquid casting material is poured into the casting cavities formed between the closely juxtaposed moulds or mould parts. After the pouring, the moulds or mould parts, now containing the casting material having been poured into them, are advanced, still in the form of a continuous string, along the casting track, during which the cooling is initiated in a cooling section. During this cooling it is important to prevent the moulds in the string of moulds from being displaced relative to each other, as this could otherwise result in deformations or cooling defects in the castings before the latter have been cooled to a shape-retaining temperature. For this reason, the length of the cooling section of the precision conveyor is often made sufficient to ensure that the castings are sufficiently cooled to be separated from the moulds in an extraction station. Especially when producing large castings, it becomes difficult to use long precision conveyors, because increased sand adhesion, produced by condensed moisture from the moulds, make the latter "stick" to the conveyor. In order to eliminate the effect of the sand adhesion, some plants are provided with a divided cooling section, in which the string of moulds is transferred to a driven conventional conveyor being synchronized with the precision conveying of the string of moulds, so that the latter is advanced without substantial displacement between the moulds occurring. When the cooling takes lace in a continuous string of moulds, the cooling section may, however, become very long, especially when producing large castings, because the moulds act as heat insulation. For this reason, the prior art has comprised attempts to shorten the cooling time by during the cooling step removing parts of the moulds or extracting the castings with a surrounding part of the moulds. This will, however, frequently require specially constructed apparatus adapted to the particular castings being made, and is also likely to produce large quantities of dust.
Thus, the purpose of the previously known second conveyor placed in extension of a precision conveyor has predominantly been to reduce the sand adhesion on the precision conveyor, and this has--to the extent that cooling is also provided during the movement on a conventional conveyor--resulted in relatively long conveying distances and cooling times possibly also a relatively large quantity of "burnt-out" binder in the mould material. Further, it has been necessary to use relatively complicated extraction stations, especially when it is necessary to prevent the castings from coming into contact with a flexible conveyor belt. These extraction stations normally produce a considerable amount of powder and dust from crushed mould parts, that should be avoided.